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Vitamin D is often touted as a modern-day panacea that will help many ailments. A simple Internet search will find promises that vitamin D will prevent your next flu, ward off a myriad of autoimmune diseases, and oh yes, forget that Zumba class, because it will also help you shed the pounds and boost your heart health. These are unsubstantiated claims, yet to be scientifically authenticated.

Vitamin D is a fat-soluble compound that aids in calcium and phosphate absorption from the gut. While we can obtain it from supplements and food sources, our bodies can also help make our own vitamin D with the help of sunlight.

Risk factors for vitamin D deficiency include:

Obesity

Gut absorption disorders

Having dark skin

Living in a culture where skin is covered for cultural reasons

Eating a diet poor in vitamin D-rich foods such as dairy products

Vitamin D is essential for bone health and calcium metabolism. Children and adults can develop brittle and soft bones — conditions named rickets and osteomalacia, respectively — if they do not obtain enough of this nutrient.

Considering these beneficial properties, you may ask:

How much vitamin D should I take?

How long do I continue supplementation?

Can I prevent bone fractures if I take vitamin D?

While the answers to the first two questions can vary, we know that research studies are not finding an association between vitamin D intake and fracture prevention.

Vitamin D Research

In a recent meta-analysis (pooling of data from multiple studies) conducted in New Zealand, Ian Reid and his colleagues set out to evaluate whether vitamin D supplementation enhances bone mineral density. Low bone mineral density leads to osteoporosis, which is a known risk for bone fracture. Bone density is evaluated by a DEXA scan, an X-ray that measures bone density of the spine and hip regions. Twenty-three randomized controlled trials, which enrolled approximately 4,000 mostly female subjects with an average age of 59, were evaluated. The primary endpoint the researchers were looking at was the percentage of change in bone mineral density from baseline. Participants were followed for an average of two years.

The authors did not find any beneficial effects from Vitamin D in the spine and total hip bone densities. However, bone mineral density increased in the femoral neck, which is part of the total hip joint. Think of the hip joint as a ball and socket apparatus. The ball is the head of the femur, which is attached to the femoral neck and the socket, the acetabulum. So one part of the hip joint showed an increase in bone density, but the total hip joint failed to show this benefit.

In analyzing differing characteristics in the groups studied, the researchers found that those with vitamin D concentrations less than 50 nmol/L at baseline and, interestingly, those taking under 800 IU of vitamin D daily, demonstrated the most notable increases in femoral neck bone density.

What Vitamin D Research Means for You

So what does this all mean? As stated by the authors of the analysis, bone mineral density improvement in a single bone site (that is, the femoral neck) may not reduce fracture risk, and the findings may be due to a statistical artifact. Another limitation to assessing the real value of vitamin D is the simultaneous use of calcium in approximately 50 percent of the trials analyzed. We know that calcium has a positive effect on bone density; therefore, the true value of vitamin D in these studies may have been over-inflated.

The other day, I had a patient who came in with a grocery bag full of various vitamins, wanting to know my thoughts. An important note I shared with her has practical implications for everyone. Too much of a supposed good thing can be equally bad in excess. Vitamins can reach toxic levels, and vitamin D is no different. In fact, studies reveal that at high enough doses, vitamin D can actually stimulate bony breakdown (osteoclastogenesis).

Now, there are those with risk factors for vitamin D deficiency. For example, patients with bone diseases such as osteomalacia or osteoporosis, or those with chronic widespread musculoskeletal pain. In such groups, testing for vitamin D levels and supplementation, if needed, is justifiable. Overall, based on the findings of this study, along with the recommendations of the Institute of Medicine and the National Osteoporosis Society, I agree that most healthy adults in North America do not need to ascertain their vitamin D levels and do not require daily supplementation.

Mahsa Tehrani, MD, is a fellow at the George Washington University department of Rheumatology. Dr. Tehrani is board certified in Internal Medicine, and also holds a Master’s degree in Complementary and Alternative Medicine from Georgetown University. In addition, she has performed a year of oncology research at the National Institutes of Health. Dr. Tehrani has been published in numerous peer reviewed medical journals, including Blood and the International Journal of Rheumatology.

Last Updated:10/16/2013

Important: The views and opinions expressed in this article are those of the author and not Everyday Health. See More

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